Infertility afflicts 15% of the couples in the United States and in at least 10% of these cases no etiology can be demonstrated. Clinical and basic research findings support the hypothesis that fertilization failure is one of the most important disorders of fertility. Egg quality, sperm motility, sperm concentration, abnormal sperm morphology and surface bound antibodies are some of the factors affecting gamete interaction. Sperm microinjection is a relatively new technique that involves the microsurgical placement of the sperm cell within the egg, using a glass holding pipette to stabilize the egg, and a sharp injection pipette to deliver the sperm cell across the egg investments. The overall objective of this research is to develop sperm microinjection as a viable in vitro fertilization method and obtain live offspring from the transfer of microsurgically fertilized rabbit oocytes. The specific aims of this project are: (1) to determine whether capacitation of sperm is necessary to achieve fertilization and subsequent embryonic development via microinjection, (2) to determine ideal microsurgical placement of sperm, ooplasm or perivitelline space in order to achieve fertilization and subsequent development, (3) to fertilize oocytes by microinjection of sperm recovered from the perivitelline space of freshly in vivo fertilized rabbit zygotes, (4) to fertilize zona free rabbit oocytes using a very low number of sperm cells (4-6) with micromanipulative guidance using microvolumes to affect sperm-egg approximation, (5) to determine a parthenogenetic activation index for rabbit oocytes due to the injection process, and (6) to understand and characterize pertinent facets of the intricate mechanisms governing mammalian fertilization.